"Rise and shine, Mr. Freeman. Rise and shine. Not that I wish to imply you have been sleeping on the job. No-one is more deserving of a rest. And all the effort in the world would have gone to waste until... well, let's just say your hour has come again. The right man in the wrong place can make all the difference in the world. So, wake up, Mr. Freeman. Wake up and smell the ashes."

Five years in development, with an estimated cost of $40m, Half-Life 2 was a gigantic game before it was even released. In the background lurked its massively acclaimed predecessor, a first-person shooter that dragged the genre out of its young, dumb twitchcore roots, producing an experience of depth and resonance. Half-Life took a crowbar to the staid narrative conventions of single-player adventures, providing a completely consistent first-person experience. Gordon never talks and we never see anything that Gordon isn't viewing in real-time – suddenly ten years of cut-scene development was struck asunder.Half-Life 2, with its protracted development period, its tie in with the construction of Valve's controversial Steam distribution engine, and the huge weight of expectations on its digital shoulders, could have been a bloated disaster. But from the moment Gordon is plucked from stasis to face the Combine, it is clear Valve has complete control over this intricately realised universe. City 17, Ravenholm, Nova Prospekt – these are nightmarishly complete visions of a post-apocalyptic hell. Inspired by Eastern European architecture, and surely the political turmoil suffered in the region over the last two decades, Bulgarian art director Viktor Antonov created a vision of a grand society in collapse, the Combine monsters looming over the landscape like monstrous insects around a carcass.

But within it all, there was always humanity. The relationship with Alyx Vance, the return of Barney Calhoun and Dr. Isaac Kleiner, lots of great, genuinely funny dialogue. Then Dr. Wallace Breen, the collaborator, so much more than just a one-dimensional bad guy – a walking satire on politics, personal ambition and the rhetoric of suppression.

And everything else. Blistering action, heart-stopping set-pieces, (literally) ground-breaking physics, bleeding edge AI… Half Life 2 was like a mega-budget disaster movie, written by George Orwell and directed by Andrei Tarkovsky. As Greg puts it, "Half Life 2 always felt like the European arthouse answer to the Hollywood bluster of Halo and Call of Duty. Yes, there is all the visceral combat you would expect from a first-person shooter but Half Life 2 interspersed this with slower-paced narrative sections that allowed you to breathe and take stock of your surroundings. And what surroundings they were. City 17, in particular, is one of gaming's most evocative locations. Your assailants too were way above the grunts seen in other shooters of the time. The best game of the decade? World of Warcraft wins my vote but Half Life 2 is an undoubted classic and if any other game had to win I'm glad it was this."

And from Jack, "Making a worthy follow-up to Half-Life must have been a tremendously daunting task - so it's no surprise Valve took their time. But the anticipation and hype that a six-year wait created was, for once, more than satisfied upon the game's release. Half-Life 2 once again pushed the envelope for the genre, and set a new high watermark for FPS narrative. I remember being shown a brief three minute clip of the Gravity Gun back in 2003 - interacting with your environment like that felt like a huge step forward at the time. I played it through again only a few months ago, and it still stands up to scrutiny in 2009. Perhaps not my favourite game of the decade, but certainly one that deserves to hold top spot."

Half-Life 2 is the game of the decade, not just because it's good, but because it encapsulates so much of what mainstream gaming has been trying to do for the last ten years; the aspiration to create believable, physically accurate worlds, then to make us a part of them. The narrative and technical achievements of this game and its episodic follow-ups have been equaled, perhaps, but not significantly bettered. We may see Half-Life's usurper in the coming decade – we may witness the next quantum shift in the medium. It will be fun getting there. This is why we play videogames, after all.

So here we go then. This is the day one of our Gamesblog Top 50 Games of the Noughties countdown. Today we're listing 50 to 31. Remember this is a games of the decade list so even getting in the top 50 is an achievement. Having said that I expected Halo 3 to do a little better. And LittleBigPlanet too. I should have argued louder about the latter but I was saving my effort for higher up the list. Plus, of course, the titles and where they got placed are heavily based on your votes. Anyway, on with the show..